Initially, I just purchased online, but ordered the wrong part. I called and talked to a real person, who helped me order the correct part and offered a reasonably priced return shipping label. That was a welcome change from other recent online purchase interactions.
Milton 1/4" FNPT Female P-Style Coupler 1803
This Milton P-Style Coupler features a 3/8" basic flow size, a maximum of 300 PSI, and airflow of 68 SCFM. In addition, this coupler comes complete with a Buna-N seal for superior strength and reliability. P-Style couplers are made to last with heavy-duty steel bodies and include 8 locking balls for better retention of plugs.
Features
• 1/4" FNPT Female P-Style coupler
• 3/8" basic flow size
• 300 PSI Max
• Buna-N seal
• Heavy-duty steel body
• 8 locking balls for plug retention